Isocitrate dehydrogenase (IDH) is a key family of enzymes found in cellular metabolism. They are NADP+/NAD+ and metal dependent oxidoreductases of the enzyme class EC 1.1.1.42. The wild type proteins catalyze the oxidative decarboxylation of isocitrate to alpha-ketoglutarate generating carbon dioxide and NADPH/NADH in the process. They are also known to convert oxalosuccinate into alpha-ketoglutarate. Mutations in IDH1 (cytosolic) and IDH2 (mitochondrial) have been identified in multiple cancer types including, but not limited to, glioma, glioblastoma multiforme, paraganglioma, supratentorial primordial neuroectodermal tumors, acute myeloid leukemia (AML), prostate cancer, thyroid cancer, colon cancer, chondrosarcoma, cholangiocarcinoma, peripheral T-cell lymphoma, and melanoma. (See L. Dang et al., Trends Mol. Med., 2010, 16, 387; T. Shibata et al., Am. J. Pathol., 2011, 178(3), 1395; Gaal et al., J. Clin. Endocrinol. Metab. 2010; Hayden et al., Cell Cycle, 2009; Balss et al., Acta Neuropathol., 2008). The mutations have been found at or near key residues in the active site: G97D, R100, R132, H133Q, and A134D for IDH1, and R140 and R172 for IDH2. (See L. Dang et al., Nature, 2009, 462, 739; L. Sellner et al., Eur. J. Haematol., 2011, 85, 457).
These mutant forms of IDH are shown to have a neomorphic activity (also known as a gain of function activity), reducing alpha-ketoglutarate to 2-hydroxyglutarate (2-HG). (See P. S. Ward et al., Cancer Cell, 2010, 17, 225) In general, production of 2-HG is enantiospecific, resulting in generation of the D-enantiomer (also known as R enantiomer or R-2-HG). Normal cells have low native levels of 2-HG, whereas cells harboring these mutations in IDH1 or IDH2 show significantly elevated levels of 2-HG. High levels of 2-HG have been detected in tumors harboring the mutations. For example, high levels of 2-HG have been detected in the plasma of patients with mutant IDH containing AML. (See S. Gross et al., J. Exp. Med., 2010, 207(2), 339). High levels of 2-HG are highly associated with tumorigenesis.
Mutant IDH2 is also associated with the rare neurometabolic disorder D-2-hydroxyglutaric aciduria type II (D-2-HGA type II). Germline mutations were found at R140 in IDH2 in 15 pateints having D-2-HGA type II. Patients having this disorder also have consistently increased levels of D-2-HG in their urine, plasma and cerebrospinal fluid. (See Kranendijk, M. et al., Science, 2010, 330, 336). Finally, patients with Oilier Disease and Mafucci Syndrome (two rare disorders that predispose to cartilaginous tumors) have been shown to be somatically mosaic for IDH1 and 2 mutations and exhibit high levels of D-2-HG. (See Amary et al., Nature Genetics, 2011 and Pansuriya et al., Nature Genetics, 2011).
Thus, there is a need for small molecule inhibitors of mutant IDH proteins having a neomorphic activity for the treatment of diseases and disorders associated with these proteins.